The Environmental Determinants of Diabetes in the Young (TEDDY) study was initiated in 2004 by six clinical centers in the United States and Europe, and screened 424,732 newborns to enroll 8,669 children (2525 in Sweden) at increased HLA risk for type 1 diabetes (T1D). The primary objective of our multi-center, prospective cohort study in this renewal application is the identification of infectious agents, dietary factors, and other environmental exposures that may trigger or protect against the development of islet autoimmunity and T1D as well as celiac disease, a common co-morbidity to T1D. Enrolled infants are followed four times per year until age 4 and twice a year thereafter until age 15. In 2013, the youngest children will be 3 and the oldest 8 years of age. So far, 425 children (145 in Sweden) have developed persistent islet autoantibodies and 117 (30 in Sweden) have developed T1D. The specific aims of this renewal application are to: 1) Follow the TEDDY cohort of 8,669 high-risk children for development of islet autoimmunity and diabetes and celiac disease for 5 more years; 2) Collect all planned biological specimens and epidemiological data according to the standard TEDDY protocol with continued high retention and compliance and close monitoring of sample and data quality; 3) Perform planned laboratory analyses at appropriate times using a nested case-control study design to answer specific scientific questions and hypotheses pertinent to the TEDDY study goals; 4) Analyze and publish laboratory and epidemiological data in collaboration with the TEDDY Data Coordinating Center (funded by a separate UC4 contract), and 5) Guide the ongoing TEDDY project by participation of Sweden TEDDY clinic investigators and staff in the work of the study Steering Committee and sub-committees. These aims are crucial to the long-term scientific goals to A) to identify environmental factors that trigger or protect against the development of defined islet autoantibodies (against insulin, GAD65, IA-2 as well as ZnT8) or clinical T1D; B) to assess potential gene-environment interactions affecting development of islet autoimmunity or T1D, and to gain insight on mechanisms; and C) to collect and bank specimens for studies of T1D pathogenesis and development of biomarkers for T1D prediction. A successful study outcome should allow better understanding of the etiology and pathogenesis of islet autoimmunity and T1D, thereby guiding development of new strategies to prevent, delay, or reverse the disease.